May 14, 2014 1630 UTC Day 1 Convective Outlook

…THERE IS A SLGT RISK OF SVR TSTMS FROM THE MID/UPPER OH VALLEY AND LOWER GREAT LAKES TO GULF COAST STATES…

…SUMMARY…
ISOLATED SEVERE THUNDERSTORMS ARE LIKELY ACROSS PARTS OF THE LOWER MISSISSIPPI…TENNESSEE…AND OHIO VALLEYS THIS AFTERNOON INTO TONIGHT. DAMAGING WIND SHOULD BE THE PRIMARY HAZARD. HOWEVER…A FEW TORNADOES AND LARGE HAIL WILL ALSO BE POSSIBLE…ESPECIALLY FROM PARTS OF TENNESSEE AND KENTUCKY INTO FAR SOUTHEAST INDIANA…MUCH OF OHIO…AND WESTERN PENNSYLVANIA.

…SYNOPSIS…

A HIGH-AMPLITUDE BLOCKING PATTERN WILL PERSIST OVER NORTH AMERICA THROUGH THE DAY ONE PERIOD WITH THE PRIMARY FEATURE OF INTEREST BEING A FULL-LATITUDE TROUGH LOCATED OVER THE CENTRAL PART OF THE CONTINENT. WITHIN THIS BROADER-SCALE PATTERN…A VORTICITY MAXIMUM AND ASSOCIATED 50-60 KT JET STREAK AT 500 MB WILL EJECT NEWD FROM THE BASE OF THE PARENT TROUGH THROUGH THE LOWER MS INTO OH VALLEYS IN ADVANCE OF AN UPSTREAM VORTICITY MAXIMUM DIGGING EQUATORWARD OVER THE UPPER MS VALLEY. THE GEOSTROPHIC RESPONSE TO THE FORMER VORTICITY MAXIMUM AND ATTENDANT 500-MB JET STREAK WILL BE MANIFEST IN THE FORM OF AN INTENSIFYING 850-700-MB WIND FIELD FROM THE MID SOUTH/TN VALLEY TO OH VALLEY LATER TODAY INTO TONIGHT.

AT THE SURFACE…LOW PRESSURE OVER NRN MS WILL DEEPEN SLIGHTLY TODAY PRIOR TO UNDERGOING MORE SUBSTANTIAL INTENSIFICATION TONIGHT AS IT DEVELOPS NNEWD ALONG AN ASSOCIATED QUASI-STATIONARY FRONT TO NERN IND/NWRN OH BY 15/12Z. MEANWHILE…A TRAILING COLD FRONT WILL ADVANCE EWD THROUGH THE LOWER MS VALLEY AND CNTRL GULF COAST STATES.

…GULF COAST STATES TO MID/UPPER OH VALLEY AND LOWER GREAT LAKES THIS AFTERNOON INTO TONIGHT…

12Z SOUNDINGS ACROSS THE PRE-FRONTAL WARM SECTOR INDICATE THE PRESENCE OF A MOIST AIR MASS CHARACTERIZED BY DEWPOINTS OF 60-70 F AND LOWEST 100-MB MEAN-MIXING RATIOS OF 11-13 G/KG. WEAK MIDLEVEL LAPSE RATES AND THE PRESENCE OF EXTENSIVE CLOUDS /AT LEAST ALONG THE IMMEDIATE SURFACE FRONTAL INTERFACE/ WILL TEMPER THE DEGREE OF DESTABILIZATION TODAY. WHERE STRONG BOUNDARY LAYER HEATING CAN OCCUR…AFTERNOON MLCAPE VALUES WILL APPROACH 1000-1500 J/KG.

DCVA ASSOCIATED WITH VORTICITY MAXIMUM IN CONJUNCTION WITH A STRENGTHENING WAA REGIME ATTENDANT TO THE DEVELOPING LLJ WILL FOSTER AN INCREASE IN TSTMS ACROSS THE SLIGHT RISK AREA TODAY. LATEST CONVECTION-ALLOWING MODEL GUIDANCE SUGGESTS THE FORMATION OF A BROKEN CONVECTIVE BAND EVOLVING FROM THE VICINITY OF THE SURFACE LOW OVER WRN/MIDDLE TN SWD INTO MS/AL WITH ADDITIONAL…MORE RANDOM TSTM ACTIVITY INTENSIFYING BY AFTERNOON WITHIN THE WAA REGIME OVER KY/IND/OH.

THE RESPONSE TO THE DEEPENING SURFACE LOW…AND TO A LESSER EXTENT…THE PRESENCE OF A BACKDOOR FRONT OVER WRN NY/PA INTO WV WILL RESULT IN VERTICALLY VEERING WIND PROFILES ACROSS THE WARM SECTOR WITH DEEP-LAYER SHEAR BECOMING SUFFICIENT FOR SUPERCELL AND/OR BOWING STRUCTURES. DAMAGING WIND GUSTS AND PERHAPS A FEW TORNADOES WILL BE THE PRIMARY HAZARDS…ESPECIALLY WITH STORMS FORMING NEAR AND AHEAD OF THE MIGRATORY SURFACE LOW WHERE LOW-LEVEL SHEAR AND FORCING ARE ENHANCED. THE TORNADO THREAT MAY BECOME MOST FOCUSED LATER THIS AFTERNOON INTO EVENING OVER CNTRL/ERN OH WHERE THE STRONGEST INSTABILITY COINCIDES WITH THE INCREASING VERTICAL SHEAR. HAIL POTENTIAL WILL LIKELY BE MAXIMIZED LATER TODAY OVER ERN PARTS OF OH/KY/TN WHERE STRONGER HEATING MAY YIELD GREATER DESTABILIZATION.

WHILE DIMINISHING IN AREAL EXTENT…AT LEAST AN ISOLATED SEVERE THREAT WILL PERSIST INTO THE OVERNIGHT HOURS NAMELY OVER THE UPPER OH VALLEY OWING TO THE DYNAMIC FORCING ASSOCIATED WITH THE MIDLEVEL VORTICITY MAXIMUM AND DEEPENING SURFACE LOW.